I know there's an AAV turbo being built at the moment that'll run G40 management. I reckon it'll work very well, but I don't think it'd take 22psi of boost plus nitrous that a G40 lump with forged pistons can accomodate.

Is AAV the spi 1.3? The pistons are rediculously tough, compare them with anything else and they look like they are out of an old tractor. My car must have hammered ten bells out of the shaved ABD pistons when it blew the actuator hose off and they sustained no damage, when my mates mini detted its face off it wiped all the ring lands off his accralites in a few seconds (which are cheap though). Forged pistons are for making serious power, I think the standard head gasket would go before the standard pistons did. I guess you just get an added safety factor with forged pistons.

Yeah, suck through is a compromise, i would agree. But as for it not being a serious tuning modification? I disagree. As said, the aformentioned K70 is making 450bhp! Its a drag car, essentially, and not a daily, but it shoes the power is there too be had. Plus, plenty of old school bikes use the same method, so although not perfect, i think its still possible to get good results

Yeah I phrased it badly saying suck through wasnt a serious tuning mod, obviously top fuel dragsters use it so its not really a fair point. I was talking more in the context of that mini that was posted, where to get any power out of it you probably have to drop the compression ratio and run less timing, making it lazy off boost and really thirsty on fuel compared with a blow through setup.

Suck through setups may appear to make good power, but compare them with a similar blow through setup and there will be no contest, although like I mentioned earlyer, possibly the suck through could work very well if you went heavy with water injection.

Bikes use suck through a lot because they make mega power on not a lot of boost, and there is nowhere to put an intercooler anyway so if they are going to run them adiabatic they may as well use suck through because its easyer. But nearly all the supercharged V8's you see at the drags run suck through, and appear to make good power, but compare them with a half descent twin turbo injected setup and there is just no comparison. Although thats also part the superchargers fault as well I suppose, if I was king they would all get banned, damn engine parasites!

Edited 29 November, 201015 yr by Tommo32

I see your point. As I said, there are compromises with this set up. What does the water/meth do exactly, co the charge?

I'm far from an expert on WI, as I have never had to use it before. There are people on here that will know more about it than me. But the principal is that you atomise water into the inlet charge as it absorbs the heat energy as it evapourates, thus cooling the charge, increasing the density (more O2 molecules per unit of volume etc etc). Methonol does the same job but slightly more effectively, and also acts as a fuel (so does the water if you are good at chemistry).

As I thought. I see how the meth could be a fuel, since it's a hydrocarbon, but I can't see water as a fuel, unless it somehow disociates becoming O2 and H, which would be extremely reactive. But I don't know how this would be done in an internal combustion engine since it is done via electrolysis

Edited 29 November, 201015 yr by prankstar2003

H20 is used to cool the combustion chamber and reduce knock.

Water and methanol both have a high latent heat of evaporation compared to petrol.

Latent heat is the energy required to change the state from a liquid to a gas.

Petrol is around 293 KJ/Kg

Methanol is around 1100 KJ/Kg

and Water is around 2257 KJ/Kg

The energy required to drive the change from a liquid to gas is taken in the form of heat from the combustion chamber, piston crown etc.

I like the idea of a draw through carb and supercharger.

The fuel evaporation will cool the charge and the fuel will help seal the rotors in the SC and improve efficiency.

Obviously Fuel injection is the way to go, but for a low cost project I think it would be hard to beat.

Turbos are not without parasitic losses.

They are a restriction to exhaust flow and increase pumping losses.

The fuel also helps to lubricate the rotors too, improving the life span of the charger. I'm really tempted to have a go at one of these, but as I've said, it's the space which is the issue. Any ideas?

If you have the know how then running a set of bikecarbs with a turbo/supercharger is stupidly easy to do (id say even a novice hobby mechanic would get the jist pretty quickly) . I'm about half way through my parts list and design and after winter ill be dealing with fabricating some of the parts needed.

As Tommo said the stock aav pistons are pretty solid and do seem to survive a hammering with the HG normally failing well before there is even a risk to the pistons.

The Htt polo was running an eaton with a Ren5 turbo carb (and a lot of custom pipework), its still in existence but not in supercharged form (and last know was rotting away in a garage in port talbot) as it shattered the pulley.

Edited 29 November, 201015 yr by Cymro

What does your parts list consist of then

All good technical stuff in this thread now!

Going back to the water as a fuel thing, it goes slightly beyond the obvious (and beyond my general chemistry knowlege), however I will post some info up which is not my own, merely stolen from Robert Harris.

"During combustion - water - H2O ( present and formed ) is extremely active in

the oxidation of the hydrocarbon. The predominate reaction is the following:

OH + H ==> H2O

H2O + O ==> H2O2

H2O2 ==> OH + OH

Loop to top and repeat.

The OH radical is the most effective at stripping hydrogen from the HC

molecule in most ranges of combustion temperature.

Another predominate process is the HOO radical. It is more active at lower

temperatures and is competitive with the H2O2 at higher temps.

OO + H ==> HOO

HOO + H ==> H2O2

H2O2 ==> OH + OH

This mechanism is very active at both stripping hydrogen from the HC and for

getting O2 into usable combustion reactions."

"As can be seen above, water is most definitily not only not inert but is a

very active and important player in the combustion of hydrocarbon fuel.

Ricardo and others have documented that under certain conditions ( normally

supercharged ) water can replace fuel up to about 50% and develop the same

power output, or that the power output can be increased by up to 50% addition

of water. This conditions were investigated by NACA and others for piston

aircraft engines. It is important to note that these improvements came at the

upper end of the power range where sufficient fuel and air was available to

have an excess of energy that could not be converted to usable pressure in a

timely manner."

As for the parasitic losses of turbos, of course there is an exhaust restriction, but at least it gets its energy from a waste source, rather than actually sapping energy which otherwise would be directly used to power your car.

There are many people that blow through bike carbs, but for a car is seems just too messy having 4 carbs, tuning them all to work right would not be easy.

I considered an RS turbo carb when I did my car, and I would have used one of those had it not been for the fact I already had an R5 carb. IIRC they are a twin choke weber. I just think that people are getting a bit giddy for suck through when blow through is no harder if you get a carb thats designed for the job. Dont forget that you want to richen the mixture significantly when it comes on boost, running about 12.5:1. I'm not sure how you go about that with a suck through method, but I'm guessing that most applications dont run enough boost to warrent the extra fuelling, or a compromise is found between a bit lean on boost and a bit rich off boost. Probably only really a problem with turbo's as the boost is load dependant.

H2O2 is hydrogen peroxide.

I think the only RS Turbos that used a carb were retro fitted turbo conversion kits from Turbo Technics.

All factory RS turbos were Mechanical injection, except Fiesta RS Turbos which where EFI.

Well....as we're talking combustion theory:

Can't cite this as I don't know the source.

In a running engine, air is drawn in at some ambient temperature, and this

air then begins to pick up heat from the hot internal engine surfaces it

contacts. Finally it enters the actual cylinder, where is it heated by even

hotter surfaces. Trapped there, it is heated again by the process of

compression.

In this heating process, some little discussed chemical reactions begin to

occur in the fuel. Called preflame reactions, these take the form of slow,

partial breakdown of the least durable types of fuel molecule. Fuel

hydrocarbons have three basic forms; straight carbon chains, branched

chains, and ring structures. Temperature is a measure of average

molecular activity, but there are always some gas molecules moving

significantly faster than the others. These faster moving molecules hit and

break some of the less durable fuel molecules, dislodging some of their

more weakly bonded hydrogen atoms. This released hydrogen (H+) is very

reactive (normally diatomic travel in bonded pairs, but this is atomic

hydrogen) and instantly pairs with an oxygen from the air to form what is

called a radical (-OH), a chemical fragment that is highly reactive because if

contains and unpaired electron. Its attraction for the missing electron is so

great that it can snap one out of other chemical species it happens to

collide with, thereby breaking it down as well.

At some point in the compression stroke, the spark ignites the mixture and

combustion begins. The burned gases, being very hot, expand against the

still unburned charge, compressing it outward into the squish band. This

compression rapidly heats the unburned charge even more, accelerating

the preflame reactions in it. As a rule of thumb, the rate of chemical

reaction doubles every seventeen degrees F. All this while, the population

of reactive molecular fragments radicals is increasing in the unburned

endgas. If this process of heating takes long enough, and reaches a

temperature high enough, this population of radicals becomes great

enough that its own reaction rate one radical creating more and more

through further reactions accelerates into outright combustion. This is

autoignition.

Now why does this heated, chemically changed endgas detonate instead of

simply burning? The fuel in the endgas is no longer ordinary gasoline. The

preflame reaction that have taken place in it have changed it into a

violent explosive much like a mixture of hydrogen and air, or acetylene

and oxygen. It is in a hair-trigger state, being filled with reactive

fragments from preflame reactions. When it autoignites spontaneously,

combustion accelerates almost instantly because the material is so easily

ignited now. The combustion front accelerates to the local speed of sound,

igniting the material it passes through simply by suddenly raising its

temperature, through the shock wave it has now become.

Edited 29 November, 201015 yr by varnish

I see your point between making the choice between suck and blow through. It's finding the blow through carba which is the problem. And then having to seal them, which could be a problem too. Personally I would say blow through gives the better results, but suck is easier. That's the compromise I guess

Interesting stuff about the water chemistry. I shall have to ask some of the chemistry teachers in the department about that.

If you have the know how then running a set of bikecarbs with a turbo/supercharger is stupidly easy to do (id say even a novice hobby mechanic would get the jist pretty quickly) . I'm about half way through my parts list and design and after winter ill be dealing with fabricating some of the parts needed.

Please explain how this is 'stupidly easy to do'

I guess it could be providing you have a set of bike carbs that can handle boost. But that alone is pretty difficult.

Well, the carbs wouldn't have to handle boost if its a suck through method, since they dont need to be sealed. The one major problem i see with this is the manifold. It would have to go from 4 carbs --> charger --> 4 inlets which I can see as being quite an issue

Drawthrough bike carbs is a pretty daft idea IMHO, just messy. As much as it hurts me to say it if you are going to run drawthrough then you are probably best with something like a SU, they are easy to tune if you know what you are doing.

I'm sure people convert bike carbs to blow through though. As they are usually a CV carb you have to run boost to the atmospheric side of the diaphrams so that the system still works, also a boost referance fuel pressure regulator stops it blowing bubbles in the float bowls. And I'm guessing they just put a massive main jet in for 'on boost' fuelling, as there is no seperate circuit for that, so that means running uber rich at times.

Varnish, I have just googled the RS turbo carb business and you are right. I never really looked into it but I just remember someone telling me that fiestas had a carb and escorts were injected. What a load of crap.

I would reccomend metro turbo carb + fuel pressure regulator. Cant really go wrong with those, plus if you want it dyno tuning there are loads of mini specialists who know what they are doing.

Well, the carbs wouldn't have to handle boost if its a suck through method, since they dont need to be sealed. The one major problem i see with this is the manifold. It would have to go from 4 carbs --> charger --> 4 inlets which I can see as being quite an issue

Yeah, thats a slight problem....

Unless you run 4 superchargers

I did find a set of carbs (think there still on ebay) that are off a turbo bike.

http://cgi.ebay.co.uk/xj650-turbo-carbs-ca...=item2eb1513401

£300 though... Is it worth it? Aswell as all the other work that would need to go into it.

Defo not a budget build, but i bet you could get some pretty decent power running that kind of setup.

Bear in mind that the injected route doesnt really cost anything. How much is a G40 inlet manifold and all the other crap that goes with it? The only problem is that its not all that easy to get the gear to map the digifant yourself.

Yeah

I reckon your onto something with a metty turbo carb and megajolt/megasquirt (whichever it is)

What did you do in regards to the exhaust manifold on the abd tommo?

Metro carb + injection? Surely thats unnecesary?

And as for the injection not being pricey, thats true. But you have highlighted the major problem there in your post - setting up the injection system. It just doesnt interest me to fiddle arround with injection atm.

Would love to build a carbed forced induction monster on a budget, just to say you'd done it. Yours sounded like fun tommo, any pics of the work, such as mani etc?

Metro carb + injection? Surely thats unnecesary?

Where's that idea coming from?

Nobody said that

Its this stupidly easy....

For bike carbs you use blow through as they dont need to be inside a sealed housing, when you build the plenum you add in a pressure refrence (pitot) that then fits to the top vents on the bike carbs. In turbo bikes its normally a bit of pipe with a small hole that sits in the middle of the air flow, but the method in the picture below works just as well.

This is the main basis...

As for parts the only things I'm short of is the exhaust manifold for the turbo and an intercooler, everything else will be fabricated or machined, I've got a saab 9000 LPturbo and pipework lying around (have got a spare saab intercooler as well but not sure if its will fit).

Edited 30 November, 201015 yr by Cymro

Metro carb + injection? Surely thats unnecesary?

Where's that idea coming from?

Nobody said that

Yeah

I reckon your onto something with a metty turbo carb and megajolt/megasquirt (whichever it is)

What did you do in regards to the exhaust manifold on the abd tommo?

I thought thats what you were saying here

Megajolt is mappable ignition

Its this stupidly easy....

For bike carbs you use blow through as they dont need to be inside a sealed housing, when you build the plenum you add in a pressure refrence (pitot) that then fits to the top vents on the bike carbs. In turbo bikes its normally a bit of pipe with a small hole that sits in the middle of the air flow, but the method in the picture below works just as well.

This is the main basis...

As for parts the only things I'm short of is the exhaust manifold for the turbo and an intercooler, everything else will be fabricated or machined, I've got a saab 9000 LPturbo and pipework lying around (have got a spare saab intercooler as well but not sure if its will fit).

So, following the path of the ait, that goes

Turbo-->plenum-->bike carb --> unknown gubbins (the ally bit with those black pipes on) --> head? That simple?

What is that unknown piece of gubbins between the carbs and the head, with those pipes?

And that pipe coming 'up' of the plenum is the pressure regulator?